Alteration of lead silicate glasses due to leaching in heated acid solutions

Leaching processes were studied for lead glasses having a composition similar to that of certain archaeological materials (66 wt% PbO) to determine the mechanism of the structural evolution. The glasses were leached in two static acid media (HNO3 and CH3COOH, pH 2) at 90 °C for 35 days. Analyses were undertaken of the leaching solution (pH, inductive coupled plasma–atomic emission spectrometry) and of the bulk glass (scanning electron microscopy–energy dispersive X-ray spectrometry, Rutherford backscattering spectrometry, Raman). Results show that in both acids, up to 1 day a silicon-rich surface layer is formed via typical diffusion processes. This process continues up to 35 days in the case of acetic acid. In nitric acid, one observes a stabilisation of this layer and an increase in the metal content. In both cases, Raman data are used to interpret the structural evolutions which occur in the ‘gel’ phase.